genetics - monohybrid

Genetics – Monohybrid Teacher’s Guide

1.0 Summary The Monohybrid activity is the fifth core activity to be completed after Mutations. This activity contains four sections and the suggested time to complete the activity is 50-60 minutes. Time will vary with student ability.

2.0 Learning Goals

Driving Question: Do traits really skip generations?

Monohybrid focuses on the use of Pedigrees and links them to representations of gametes, meiosis, and fertilization. Students investigate models of inheritance while learning how to create and analyze Punnett squares and Pedigrees.

Part One: Introduction to Pedigree teaches students how to use Pedigree tools to create and analyze pedigrees.

Part Two: Meiosis, Pedigrees and Punnett Squares, Oh My! makes connections between independent assortment in meiosis, random selection in fertilization, predictions made with Punnett squares, and breeding experiments that use Pedigree tools.

Part Three: Studying Patterns of Inheritance Using Pedigrees and Punnett Squares guides student reasoning as they determine probabilities of inheritance.

Part Four: An Inheritance Puzzle requires students to put everything learned in the previous three parts together in order to solve a puzzle.

Learning Goals

• Students will learn how to create and use Punnett squares. • Students will learn how to create and read a Pedigree chart. • Students will compare and contrast Punnett Squares and Pedigree Charts. • Students will predict possible phenotypes of dragon traits using Punnett

Squares and Pedigrees. • Students will understand that independent assortment in meiosis and random

selection in fertilization are together responsible for genetic variation. • Students will know that these are tools that geneticists use to identify the

dominant and recessive patterns of traits in organisms. • Students will know that breeding organisms for specific traits can produce

desired phenotypes. • Students will understand that the variety of phenotypes within a large number

of offspring is the result of the breeding of two parents and of random selection at fertilization (sexual reproduction).

• Students will be able to use probabilities and Punnett squares to estimate the distribution of phenotypes among offspring of parents with known genotypes.

Teacher’s Guide: Monohybrid of 16

Additional Teacher Background

In this activity, students will learn to create and interpret Punnett Squares and Pedigree Charts. It is important that they understand that in a Punnett Square for autosomal traits, it is impossible to determine the gender of the offspring; therefore, probability numbers are established for the possible outcome of all offspring, not gender specific. If they are using a Punnett Square to investigate a sex-linked trait, they should understand that the probability is that one-half of all offspring are male and one-half are female; therefore when they state the probability for an X-linked trait, they state the numbers based on gender. A pedigree chart shows how a particular trait is transmitted through generations of a family. A pedigree chart uses symbols that represent the sex of each member; circles represent females and squares represent males. A key identifies the code for the trait being studied. A pedigree chart is used to understand how an inherited trait is expressed within a family. For example, some traits are sex-linked traits because their genes are part of either the X chromosome (most common) or the Y chromosome (uncommon). A pedigree chart allows the researcher to view the sex of the affected individuals within a family. It also shows patterns of dominant and recessive traits. 3.0 Standards Alignment

Alignment to National Math and Science Standards (NCTM or NSES)

Objective Standards

Students will learn that gametes are randomly selected for fertilization.

Students will understand basic concepts of probability.

Students will examine the effect of random selection on the distribution of traits.

Students will be able to use simulations to construct empirical probability distributions.

Students will explore the use of Punnett squares for understanding the combinations of allele distribution.

Students will understand and apply basic concepts of probability.

Students will learn to make predictions using Punnett squares.

Students will understand and apply basic concepts of probability.


4.0 Activity Sections

4.1 Table of Contents

This activity has 4 sections that should be done in order. The last is an assessment exercise.

Table of Contents

4.2 Introduction to Pedigree Students explore the Pedigree model, learn to use its tools and construct a key for dragon pedigrees.

An advanced organizer for this section of the activity


Jill’s pedigree indicates that she has horns. The student uses the Cross tool to breed Jill and Jack, producing 40 new dragons; the Horns characteristic is shown.


Students work through all dragon characteristics to produce a key for pedigrees; the

Tail characteristic is shown.

Key for all dragon characteristics


After investigating Jack and Jill’s chromosomes, students are asked to predict how the next generation (F2) will look before they check their predictions out by making the F2 generation.

Students are then asked to explain why traits appear to skip generations. Several additional questions are posed for students to answer.


4.3 Meiosis, Pedigrees and Punnett Squares, Oh My!

This activity introduces students to Juan and Jennifer. Students predict how certain traits are passed from parent to offspring by crossing the gametes of Juan and Jennifer. Through use of the Model, they will visualize the inheritance patterns produced by these crosses.

Step 1 Make a cross of the dragons using the X tool. Step 2: Run meiosis. Step 3: Look at the gametes of one of the dragons using the magnifying glass and answer the questions regarding the traits for legs. Step 4: Run fertilization and answer the questions. Step 5: Try It: select the gametes and run the fertilization, see what happens. Ste 6: Answer the questions. Step 7: Be introduced to Punnett Squares; practice what you learned. Step 8: Click to fill in the Punnett Squares for the trait of legs in the following screens and answer the questions. Step 9: Compare predictions of Punnett Squares with offspring in Pedigree Charts. Step 10: Click on Juan and Jennifer to see their chromosomes, find the alleles for tails, and note the genotype for both dragons. Step 11: Fill out a Punnett Square using the Genotypes (Tt x tt) Step 11: Answer a series of questions that relate to heterozygous and homozygous traits. Use the information obtained from the Models. Step 12: Compare and Contrast Punnett Square and Pedigree Charts Step 13: Made it Through; Review and Summary

Meiosis Introduction


Use the Cross tool (X) to breed the parents.

Use the magnifying glass to examine the gametes of Juan and Jennifer, and then

answer the questions.


Gametes are selected randomly with the Select Gamete button.

Random processes and probabilities are linked.


Before being introduced to the Punnett square students are asked to predict and explain what they think will happen when there are lots of offspring. Students are shown how to complete a Punnett square and make predictions about the proportions of offspring with particular traits.


Pedigree Chart showing the Legs characteristic

Note: Because BioLogica randomly generates each new cross, there is considerable variability in the numbers of offspring with the different traits. In later sections we deal with proportions that differ from what is predicted by the Punnett square.

Students practice completing Punnett squares and receive feedback.


Students answer several multiple choice and completion questions, as well as higher order questions that require a thoughtful response.

Summary Screen

4.4 Studying Patterns of Inheritance Using Pedigrees And Punnett Squares

In this activity, students will put into practice what they learned in the previous activities, with particular emphasis on predictions and probability.

Step 1: Click to view the dragons’ chromosomes. Step 2: Cross dragons using Cross (X) tool. Step 3: Notice the dominant traits in the pedigree chart and answer the questions. Step4: Continue with new parents and varying traits. Step 5: Answer probability questions. Step 6: Explanation and questions screens complete this activity.


Exploring Offspring Phenotypes

Punnett square showing George and Lucinda’s genotypes for legs: both are heterozygous. Notice that the upper-left cell of the Punnett Square is incorrect (should be LL). Students have a chance to self-correct, but BioLogica will correct them if they are unable to rectify their mistake.


After making predictions based on the Punnett squares they completed, students cross George and Lucinda to see how close their prediction was to the actual outcome.

In the task that concludes this section students must change the alleles of one of the parents in order to produce offspring that are all heterozygous for Legs, shown above. Note: Once you have crossed the parents you cannot change their alleles. If students don’t succeed initially, they must use the scissor tool to snip out all the offspring before changing the parent’s allele. Parents must be homozygous, one LL and the other ll, to produce offspring with only 2 legs.


4.5 An Inheritance Puzzle This section returns to the original focus question: “How can a trait skip a generation?” It challenges students to set up the parents’ alleles with a trait of their choosing and demonstrate under what conditions it is possible.

Introduction

Rules of the game


First step in the puzzle.

Add a male and female dragon. Use the Chromosome tool to view and change alleles. Use the Cross (X) tool to breed them. Use the Scissor tool to delete all the offspring and start again. Use the Punnett square pad to check out allele combinations anytime. Students’ entries in the Punnett square are not checked or corrected. Students have three tries to solve the problem.

Note: Once you have crossed the parents you cannot change their alleles. If students don’t succeed initially, they must use the scissor tool to snip out all the offspring before changing the parent’s allele. Parent dragons must each be homozygous for a trait. This will create an F2 generation that is heterozygous for a particular trait. Once students have completed the puzzle, they are asked to describe how they did so and which completed Punnett squares for each generation can be used to explain their results.

5.0 Student Reports Your students’ work with Monohybrid is logged and viewable on the MAC Project Web Portal at http://mac.concord.org. For each student, you can view a report containing questions and answers. The next activity that students should use is X-Linkage, which focuses on the inheritance of traits on the X chromosome using breeding experiments and pedigree analysis learned in Monohybrid.


http://mac.concord.org/

genetics - monohybrid

Documents